1. Field of the Invention
This disclosure generally relates to electric motors, and particularly to the control of electric motors in electric motor driven systems, for example, electric vehicles.
2. Description of the Related Art
A large variety of applications employ electric motors. For example, electric vehicles such as electric vehicles with battery, super- or ultra-capacitors, fuel cell and/or hybrid power sources employ electric motors in the power train to drive the traction wheels of the vehicle. Such electric motor driven vehicles may also employ electric motors to drive auxiliary devices, such as fans, compressors, blowers, moving seats and/or windows. Many other applications exist for electric motors that are not transportation vehicle related.
Electric motors may be driven using alternating current (AC) or direct current (DC) electric power. In the case of a traction motor for an electric motor driven vehicle, the electric motor is typically driven using AC power. The AC power may be supplied from a DC power source such as a battery, super- or ultra-capacitor, and/or fuel cell system. Such systems employ an inverter to transform the DC power from the DC power source to AC power for driving the electric motor. Typically, the AC power is supplied as three phase AC power at a relatively high voltage (e.g., 24VAC–400VAC).
Most motor driven applications employ a control subsystem for controlling operation of the electric motor. The control subsystem may include a microprocessor and associated memory which typically require DC power at a relatively low voltage (e.g., 2.5V–5V). Consequently, many electric motor driven systems will employ a low voltage power supply (LVPS) to transform the high voltage DC power from the DC power source to a low voltage suitable for use with the control subsystem.
There are a large variety of control subsystems and control regimes suitable for the different electric motor driven applications. Even in the relatively limited field of electric motor driven vehicles, a large number of different control subsystems and control regimes have been proposed. In almost all instances of electric motor driven systems, it is possible that power to the control subsystem may be interrupted during normal operation. In electric motor driven vehicle applications, the power train is required to resume normal torque production after low voltage dropout interruptions lasting under several seconds, for example, during periods of high torque demand. Conventional approaches may produce motor control loop stability problems, resulting in current demand surges while attempting to command full torque from an electric motor with insufficient flux. An improved motor control subsystem and control regime to address this problem is desirable.